super minor: fixed comment on line 16 (doesn't affect anything)

src/environment.ts

@@ -13,7 +13,7 @@ function lookup<T>(x: string, env: Environment<T>): T | undefined {
 }
 
 function isDefined<T>(x: string, env: Environment<T>): boolean {
-  // 1. Return a Boolean value that represents whether an environment specified in parameter `x` has a variable specified in the parameter `x`.
+  // 1. Return a Boolean value that represents whether an environment specified in parameter `env` has a variable specified in the parameter `x`.
   // TODO: YOUR CODE HERE // Hint: You can find which methods to use at: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map
 }